ZCZC SPCSWOMCD ALL
ACUS11 KWNS 230948 
SPC MCD 230948 
IAZ000-MNZ000-NEZ000-SDZ000-231545-

Mesoscale Discussion 1901
NWS Storm Prediction Center Norman OK
0348 AM CST Fri Dec 23 2016

Areas affected...Northeast NEB...northwest and north central
IA...extreme southeast MN

Concerning...Heavy snow 

Valid 230948Z - 231545Z

SUMMARY...A band of snowfall will develop and spread
east-northeastward this morning from eastern NEB across northern IA,
potentially reaching south-central/southeastern MN by midday. 
Snowfall rates should increase to near 1 inch per hour within this
band.

DISCUSSION...A midlevel trough will eject east-northeastward from
the central High Plains this morning to the Middle MS Valley by this
afternoon.  Focused ascent in the left exit region of the mid-upper
jet, combined with low-level warm advection, will support a band of
precipitation that is developing over southern NEB early this
morning and will spread east-northeastward through midday.  Though
surface observations show temperatures a few degrees F above
freezing from NEB into IA, web-bulb temperatures are near 32 F.  As
top-down saturation occurs and precipitation rates increase,
wet-bulb cooling should allow wet snow to become the dominant
precipitation type this morning.  Embedded midlevel convection could
boost snowfall rates to near 1 inch per hour through the morning,
and cold ground from the recent arctic intrusion should still allow
snow accumulations even with surface temperatures slightly above 32
F.

..Thompson.. 12/23/2016

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...ARX...MPX...DMX...FSD...OAX...GID...

LAT...LON   41999374 40709741 40739853 41049873 41989729 43139535
            43789394 43939249 43659187 42989189 41999374 

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